The invention generally relates to thermal motors using a solid material to convert thermal energy or other stress inducing sources, directly into mechanical energy. Thermal engines employing expansion of solids have been proposed in the past. For example, Jedlicka, et al U.S. Pat. No. 3,830,060 describes an engine comprising a rotor which is stressed by forces such as gravity or springs, applied near the ends of the rotor and tending to bend it and means for applying heat to the compression side of the rotor, the forces applied to the rotor are compliant so as to allow expansion of the heated side of the rotor.
An article entitled A Rubber Heat Engine by Paul B. Archibald which appeared in the March 1967 issue of Research/Development describes a heat engine using the principle that the retractive force of rubber is proportional to the absolute temperature. The Archibald engine clearly illustrates how induced stress alone produces torque. However, the Archibald engine is limited as to the materials that can be used and requires a heavy frame and thrust bearings with high bearing loads.